Thanks everyone for your suggestions. I just fitted a new BB, so I wasn't keen on replacing it already to accommodate the Octalink which requires a different (Octalink) BB. I also just replaced the chain. The bike shifts beautifully, particularly under load, and I am very pleased with everything except the absence of low gears.
As for replacing the chainrings on my current set up, would you believe the Biopace chainset is *riveted*? There is no swapping out of rings, or I would simply have gotten a smaller inside one to replace the 28.
I have calculated the potential gearing based on keeping the current chainset and simply changing the cassette to an 11-34. While it is an improvement, it is only marginal. In fact, it only provides one new low gear, 28 x 34 (22 g.i.), and the next lowest gear is *higher* than the current lowest gear. So, the only way to deliver a real new low end is by changing the chainset.
Originally Posted by halfspeed
The crankset will work. . . . .
All that aside, the real compatability issue is your bottom bracket. You aren't likely to have an Octalink BB of the right width on your current bike.
So, what you need is either a) properly selected chainrings and maybe a chain OR b) a new crankset, probably BB and maybe a chain.
You could always just replace your chainrings, but then you need to match the spacing and BCD.
Thanks for that halfspeed.
So. . . a new Octalink bb is about £22. This Deore chainset is on sale for £34. A new megarange cassette is £18. So all in I am looking at an outlay of £74 or about 150 bucks. It's more than I would like to spend but a marginal price to pay for the comfort enhancements. Yesterday's hilly 40 miles through St. Patrick's country in County Down was the clincher: low gears good!